FERGUSON, Mo. (AP) — A Missouri teenager fatally shot by police suffered a bullet wound to his right arm that may have occurred when he put his hands up or when his back was turned to the shooter, "but we don't know," a pathologist hired by the teen's family said Monday.

An independent autopsy conducted on 18-year-old Michael Brown determined that the teen was shot at least six times, including twice in the head. Brown was shot by a police officer Aug. 9 in Ferguson, touching off a week of rancorous protests in the St. Louis suburb.

Forensic pathologist Shawn Parcells, who assisted former New York City chief medical examiner Dr. Michael Baden during the autopsy, said a graze wound on Brown's right arm could have occurred in several ways.

The teen may have had his back to the shooter, or he could have been facing the shooter with his hands above his head or in a defensive position in front of his face, "but we don't know," Parcells said.

Baden said one of the bullets entered the top of Brown's skull, suggesting his head was bent forward when he suffered the fatal injury. He also was shot four times in the right arm.

Baden has testified in several high-profile cases, including the O.J. Simpson murder trial.

Brown's death heightened racial tensions between the predominantly black community and the mostly white Ferguson Police Department, leading to several run-ins between police and protesters. The governor has called in the National Guard to help and put the Missouri Highway Patrol in charge of security.